The R Project SVN R

\description{

\description{

  Old-style (S3) classes may be registered as S4 classes (by calling

  Old-style (S3) classes may be registered as S4 classes (by calling

  \code{\link{setOldClass}}, and many have been.  These classes can

  \code{\link{setOldClass}}, and many have been.  These classes can

  then be contained in (that is, superclasses of) regular S4 classes, allowing formal methods

  then be contained in (that is, superclasses of) regular S4 classes, allowing formal methods

  and slots to be added to the S3 behavior.  The function

  and slots to be added to the S3 behavior.  The function

  the S3 part of such an object.

  the S3 part of such an object.

  \code{S3Class} extracts or

  \code{S3Class} extracts or

  replaces the S3-style class.  \code{S3Class} also applies to object

  replaces the S3-style class.  \code{S3Class} also applies to object

  from an S4 class with \code{S3methods=TRUE} in the call to \code{\link{setClass}}.

  from an S4 class with \code{S3methods=TRUE} in the call to \code{\link{setClass}}.

See the details below.

See the details below.

  Also discussed are S3 <-> S4 coercion; see the section

  Also discussed are S3 <-> S4 coercion; see the section

  \dQuote{S3 and S4 objects}

  \dQuote{S3 and S4 objects}

}

}

\usage{

\usage{

  New S4 classes that extend (contain) such

  New S4 classes that extend (contain) such

  classes also have the same slot, and by default the prototype has

  classes also have the same slot, and by default the prototype has

  the value determined  by the \code{contains=} argument to

  the value determined  by the \code{contains=} argument to

  \code{\link{setClass}}.

  \code{\link{setClass}}.

  Individual objects from the S4 class may

  Individual objects from the S4 class may

  an S3 class corresponding to the value in the prototype or to an

  an S3 class corresponding to the value in the prototype or to an

  (S3) subclass of that value.  See the examples below.

  (S3) subclass of that value.  See the examples below.

  \code{S3Part()}  with \code{strictS3 = TRUE} constructs the underlying S3 object by eliminating

  \code{S3Part()}  with \code{strictS3 = TRUE} constructs the underlying S3 object by eliminating

  all the formally defined slots and turning off the S4 bit of the

  all the formally defined slots and turning off the S4 bit of the

  the object to create an object from the S4 definition of

  the object to create an object from the S4 definition of

  \code{class(object)}. This is a general mechanism to create

  \code{class(object)}. This is a general mechanism to create

  partially defined version of S4 objects via S3 computations  (not

  partially defined version of S4 objects via S3 computations  (not

  much different from invoking \code{\link{new}} with corresponding

  much different from invoking \code{\link{new}} with corresponding

  arguments, but usable in this form even if the S4 object has an

  arguments, but usable in this form even if the S4 object has an

}

}

\references{

\references{

 Chambers, John M. (2008)

 Chambers, John M. (2008)

 \emph{Software for Data Analysis: Programming with R}

 \emph{Software for Data Analysis: Programming with R}

## S3Part() applied to classes with a data part (.Data slot)

## S3Part() applied to classes with a data part (.Data slot)

setClass("NumX", contains="numeric", representation(id="character"))

setClass("NumX", contains="numeric", representation(id="character"))

nn = new("NumX", 1:10, id="test")

nn = new("NumX", 1:10, id="test")

stopifnot(identical(1:10, S3Part(nn, strict = TRUE)))

stopifnot(identical(1:10, S3Part(nn, strict = TRUE)))

m1 = cbind(group, weight)

m1 = cbind(group, weight)

setClass("MatX", contains = "matrix", representation(date = "Date"))

setClass("MatX", contains = "matrix", representation(date = "Date"))

mx1 = new("MatX", m1, date = Sys.Date())

mx1 = new("MatX", m1, date = Sys.Date())

stopifnot(identical(m1, S3Part(mx1, strict = TRUE)))

stopifnot(identical(m1, S3Part(mx1, strict = TRUE)))